The present invention relates to the field of temperature measurement, and, more particularly, to measuring temperature in an ambient space environment.
Typical spaceborne electronic systems require the temperature to be sensed at many points so that the effects of temperature can be compensated. For example, a conventional satellite based phased array antenna includes multiple stationary antenna elements in which the relative phases of the respective signals feeding the antenna elements are varied to scan an effective radiation pattern or beam in a desired direction from space. Radio frequency (RF) elements of the phased array antenna need to be compensated in view of the ambient temperature range experienced by the antenna.
A conventional approach uses resistive thermal devices (RTDS) or current mode active sensors, such as the AD590 from Analog Devices of Norwood Mass., to measure temperature. However, RTDs require complex conditioning of the low signal level, and the AD590 may require special shielding in space due to radiation susceptibility. Also, the AD590 can be susceptible to electromagnetic interference (EMI).
Additionally, both RTDs and the AD590 require the use of an analog to digital (A/D) converter to provide a digital signal representative of the sensed temperature. The use of an A/D converter increases the circuit complexity and overall costs because of the additional calibration of the A/D converter that is needed, the radiation susceptibility thereof, and decreased reliability due to the additional parts.
Thus, there is a need for reliably providing a digital measurement of temperature in space without using an A/D converter.
In view of the foregoing background, it is therefore an object of the invention to provide reliable temperature measurement in space while providing a digital signal representative of a sensed temperature, without the use of an analog to digital converter.
This and other objects, features and advantages in accordance with the present invention are provided by a space vehicle including a temperature sensitive oscillator which, in turn, includes a radiation hardened inverting gain circuit. Preferably, the radiation hardened inverting gain circuit comprises a radiation hardened comparator. The temperature sensitive oscillator including the radiation hardened inverting gain circuit is able to withstand radiation in an ambient space environment. The temperature sensitive oscillator also includes a thermistor connected to the radiation hardened inverting gain circuit so that an output frequency of the temperature sensitive oscillator varies based upon a temperature of the thermistor. Also, a frequency counter is preferably connected to the temperature sensitive oscillator for generating a digital output signal representative of a sensed temperature. The sensed temperature may be used by one or more electronic circuits connected to the frequency counter.
The frequency counter may also be radiation hardened. The radiation hardened inverting gain circuit may include a plurality of transistor gates, each having a radiation hardened structure. Also, the radiation hardened inverting gain circuit preferably comprises an output and an input, while the thermistor may be connected between the output and input of the radiation hardened inverting gain circuit. Furthermore, the input may be an inverting input.
In one embodiment, the thermistor may be collocated with the radiation hardened inverting gain circuit and the temperature sensitive oscillator may have an operating temperature range of about xe2x88x9255 to 70xc2x0 C. Alternatively, the thermistor may be remotely positioned from the radiation hardened inverting gain circuit and the temperature sensitive oscillator may have an operating temperature range of about xe2x88x9280 to 300xc2x0 C.
The space vehicle may further comprise a calibration processor connected between the frequency counter and the one or more electronic circuits. Furthermore, the space vehicle may include a phased array antenna carried by the housing wherein one electronic circuit is a phased array antenna control circuit connected to the phased array antenna.